colVars for dgeMatrix

I am working with large sparse matrices that, after some operations, can return non-sparse matrices of class `dgeMatrix`.

I must be missing something here, but when I try to get colVars for a `dgeMatrix`, I get

```
Error in MatrixGenerics:::.load_next_suggested_package_to_search(x) :
Failed to find a colVars() method for dgeMatrix objects.
```

even though `colMeans2` works just fine.

Here is some (hopefully) reproducible code:

```
m <- Matrix(nrow = 3, ncol = 6, data = rnorm(18), sparse = FALSE)
sparseMatrixStats::colVars(m)
```

PS: `matrixStats::colVars(m)` returns

```
Error in matrixStats::colVars(m) :
Argument 'x' must be a matrix or a vector.
```

and calling `as.matrix` prior to `matrixStats::colVars` is very slow on larger matrices.

Any help would be much appreciated.

Empieza reproduciendo el ejemplo con sparseMatrixStats::colVars() sobre una dgeMatrix y, después, sigue el dispatch de colVars junto con la ruta funcional de colMeans2. El problema estará resuelto cuando colVars funcione para entradas dgeMatrix sin convertir matrices grandes con as.matrix().

Escrito por el modelo de indexación a partir del texto del issue.